The Highland Outlaw by Heather McCollum

Shaw Sinclair, chief of the outcast clan of Sinclairs of Caithness in northern Scotland, has made a deal with the devil. Despite his strength and lethal skills, he needs help—specifically from a woman—to accomplish his mission to bring a bairn to safety to the coast. When he meets the brave and beautiful Alana Campbell at a Samhain Festival, he decides she’s the one.
Alana Campbell is ready to show the world she’s just as skillful with a sgian dubh as any man. Attracting the attention of the brawny chief who coerces her to join him on his journey to the coast of Scotland gives her that very opportunity. Sparks flash between them as they’re forced to act as husband and wife to accomplish the deadly mission. However, when secrets threaten to tear them apart, they have to decide if their differences outweigh the reality of their feelings…